scsi: mpt3sas: make function _get_st_from_smid static

The function _get_st_from_smid is local to the source and does not need
to be in global scope, so make it static.

Cleans up sparse warning:
symbol '_get_st_from_smid' was not declared. Should it be static?
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/mpt3sas/mpt3sas_base.c

@@ -888,7 +888,7 @@ _base_async_event(struct MPT3SAS_ADAPTER *ioc, u8 msix_index, u32 reply)
 	return 1;
 }
 
-struct scsiio_tracker *
+static struct scsiio_tracker *
 _get_st_from_smid(struct MPT3SAS_ADAPTER *ioc, u16 smid)
 {
 	struct scsi_cmnd *cmd;